Apparatuses which need to have the function of detecting the location of a metal body are, for example, metal detectors and game machines. By way of example, some of the game machines are such that a metal body, e.g., a metal ball is moved within a specified space which has been set in the game machine, and whether or not a prize is won is determined in accordance with the movement of the ball. A typical example of such a game machine is, for example, a "pachinko" (Japanese upright pinball) game machine with which a game player causes a metal "pachinko" ball to move down within a space held between parallel planes and provided with a large number of obstacles.
The "pachinko" game machine has a panel which defines the space for moving the "pachinko" ball, a glass plate which covers the panel at a fixed interval therefrom, and a projectile mechanism which functions to project the "pachinko" ball to the upper part of the panel. The "pachinko" game machine is so installed that the panel extends substantially in the vertical direction. The panel is formed with a plurality of safe, holes each of which serves to make a hit when the "pachinko" ball has been led thereinto and driven out of the panel, and a single out hole into which the "pachinko" balls having failed to enter the safe holes are finally gathered to be driven out of the panel. Besides, a large number of pins (or nails) are planted on the panel substantially perpendicularly thereto in the state in which they protrude from the panel to a distance corresponding to the diameter of each "pachinko" ball, in order that the "pachinko" ball falling along the panel may frequently collide against the pins to have its moving direction altered. The pins are arranged on the panel in a predetermined distribution in which, while altering the moving direction of the colliding "pachinko" ball, they lead this ball so as to proceed toward the safe hole in some cases and to miss the safe hole in other cases.
Owing to the construction as stated above, the "pachinko" game machines come to have individualities, such as a machine in which it is easy to register hits and a machine in which it is difficult to resister hits, depending upon the slight differences of the respective machines in the arrangement and inclinations of the pins. Even identical machines involve such differences as having safe holes with a high hit rate and safe holes with a low hit rate. Moreover, the differences are among the machines are considerable.
In a game center or the like where the game machines of this type are installed in large numbers, knowledge of the individualities of the respective game machines is important for management regarding the profit administration and customer administration of the game center. By way of example, when many of the machines resister hits excessively, the game center side suffers a loss, whereas when all the machines are difficult to resister hits on, customers come disinterested, which is unfavorable to business. Accordingly, it is necessary to know the individualities of the respective game machines which are installed in the center.
For such a purpose, it is practised to detect the moving courses of the "pachinko" balls in the "pachinko" game machine. In the official gazette of Japanese Patent Application Publication No. 3560/1989, for example, there is disclosed an apparatus equipped with an upper sheet and a lower sheet which have a pair of contacts. This technique senses the existence of the "pachinko" ball in such a way that the "pachinko" ball gets on the upper sheet and depresses it, whereby the pair of contacts come into touch.
With the prior-art apparatus, however, since the sheets have the pairs of contacts, they are restricted in arrangement, and they can be arranged only along the passages of the "pachinko" balls. It is therefore impossible to detect the motions of the balls from the perspective of the whole panel. This results in a difficult problem of detecting, for example, how the balls enter the safe holes and the out hole.
In addition, since the detection is based on the physical touch of the pair of contacts, it can take place in some moving states of the ball that the depression of the sheet becomes too weak to bring the pair of contacts into touch, so the motion of the ball is not detected. Besides, inferior touches can occur due to the wear, corrosion etc. of the pair of contacts. Further, the erroneous touch of the pair of contacts can be incurred by a vibration or the like or by chattering. For these reasons, the apparatus lacks reliability.
Another problem is that, since pressure applied by the ball is utilized, the motion of the ball is easily affected.
Such problems can be encountered, not only in the "pachinko" game machine, but also in different machines. It is accordingly desired to overcome these problems.